Process for producing citric acid by means of fermentation



Patented July 31, 1928.

UNITED STATES ATENT forrics.

JOSE! SZ'UCB, Oil VIENNA, AUSTRIA, ABBIGNOB 1'0 HONTAH- m INDUSTBIALWEBK] VORHAIIS JOE. DAV. amazon, PRAGUE, OZIOEOBLOVAKIA, A. OOIPANY .OI'

CZECEOBLOVAKIA.

P300388 PRODUCING CI'IBIO AOID BY mums OI I'WLTIOH.

f This invention relates to a process for producing citric acid by means of fermentation. My process consists in cultivatin citric acid producers on molasses at a re atlvely 5 low tem erature, that is to say between the limits 0 and ,C., selecting cultures adapted for conductin the citric ac d fermentation without pro notion of oxal1c acid and growin the selected cultures upon a 10 culture medium made u from molasses.

It is known that un or appropriate circumstances certain fungi, particularly certain species of the genera citromyces, mucor, as er-gillus and penicillium, produce citric ac1d to .a rather large extent. But the weak activity of the fungi and the relatively long period of time required for fermentat on 1nvolve great risk of infection. For th s reason experts seem nowadays to incline to the opinion that for producing citric acid by fermentation on an industrial scale, solid (jelly-like) culture media are indispensable, since by the use thereof infection is localized and formation of acid is thought to be 25 accelerated. Indeed, for a long time it has been known to sow certain specles of Aspergillus and Mucor on solid culture media of an area as large as possible, as the m celium grows thereon not only very rapi ly, but so also uniforml and to a large extent. But agar-agar an like substances appropriate for use as essential constituents of such gelatinous culturemedia, are rather expensive and therefore this method of roduc-ing 85 citric acid is ver uneconomica Trials have also been ma e to overcome the risk of infection by using artificial combinations of inorganic nutritive salts with additions of carbohydrates for nutrient solutions. Also 40 with such liquid culture media the infection by yeast or bacteria is considerably lessened in comparison with the natural nutrients containing carbohydrates of direct vegetable origin, as are frequently used in the fermentation industry, but also in this case industrial exploitation is impeded by the high costs.

Now I have found that there is no necessity' of employing as acid producers exactly determined, morphologically definable species of the fungi used for this purpose, that is of the genera citromyces, mucor, aspergillus and penicillium, but that it is possible temperature.

the most suitable races of Citromyces, Mucor does not rise consi No Drawing. Application Med December 4, 18M, flerlal No. 758,808, and in Austria December 19, 1988.

to cultivate, b appropriate selection races of all the sai kinds, bymeans of which races citric acid may be successfully roduced even when molasses is employed as nutrient medium.

It has for instance been stated by several investigators, that As gillua niger as a rule produces oxalic acid, which fact can be fully confirmed. But I have found that certain races of said s ecies also produce citric acid and will pr uce citric acid only, if the temperature is maintained within certain limits and if appropriate nutrients are employed. Nevertheless such races will not show any special morphological characteristics. All that. is required is to select the most suitable races from the plurality of the others by the known methods of m cologica-l analysis, for instance b single ce l-culture, while com aring experimentally the capacity of pr ucin citric acid at relatively low 11 like manner by selecting and Penicillium, cultures can be arrived at, by means of which also in liquid culture media, especially in molasses, a satisfactory yield of citric acid is obtainable, rovided that the suitable conditions of cu ture are maintained. In contradistinction to this re-. sult the species heretofore used for producing citric acid, when employed in solutions of molasses of such concentration, as is indispensable for obtaining a satisfacto yield, will grow irregula-rl and the morbi ly developing cover will slnk 'down.

In pro ucmg citric acid from molasses by said selected fungi a good yield can even be obtained without special attention being required for keeping up perfect sterility during operations, provlded that the fermentation is conducted at relatively low temperatures. The tem erature most favorable for this purpose 1s, e. gillus about 20 centigrade. lf during the entire time of fermentation with races selected from Aspergillus the temperature erably above 20, not

for Asper-.

only the highest yield is obtained, but also a the risk of mfection is most efiicaciously obsubsequent generations. If on the other hand the fungus is cultivated at higher temperature, it grows very well and reduces much citric acid, but the latter 1s transformed into oxalic acid by further oxidation in accordance with and at the rate of the'rise of temperature. Besides the spores deriving from fun i, which in one or several generations had een cultivated at higher temperature, gradually lose their capability of producing a sufiicient amount of citric acid, even when sown on a most appropriate cul ture medium. Finally also the risk of infection considerably increases by rise of tem erature. Nevertheless, if care is taken to o serve'strictly sterile conditions, cultivation may be carried on even at hi her temperatures, the time of fermentation being considerably shortened thereby.

As molasses from its origin contains all the substances necessar for fermentation yielding citric acid, an as it is relatively cheap, the described method of producing citric acid represents a process suitable to be worked on a commercial scale.

Under certain circumstances it may be advantageous to render the salt contents of the molasses more suitable or favorable b appropriate additions, for instance by addition of phosphates, or on the other hand to liberate the molasses by refinin of certain ingredients, particularly 0 certain salts, e. g. of potassium salts. In all other respects the conditions for operatin are those already known and practised. referably the liquid nutrient is spread by pouring it into open flat pans so as to offer a eat surface to the growth of the fun he height of the layer is also limited by t e requirement, that the liquid has to be well acidulated in order to be protected from infection.

The recovery of the citric acid from the nutrient liquid can be effected in known manner. The citric acid may be neutralized during fermentation within the nutrient solution at the rate of its generation b I means of alkalies or earth alkalies, but suc neutralization is not indispensable. Beside other earth alkalies barium is also appropriate for this purpose. Neutralization of the nutrient solution by means of barium, be. it in the form ofan oxide, of hydroxide orof a carbonate, offers the advantage, that the citrate of barium is at low temperature less soluble than calcium citrate and therefore will precipitate in the cold. The barium may thereafter be again completely removed in the form of sulphate. I use the term citric acid producer in the following claims to include the fungi of the four groups Citromyces, Mucor, Aspergillus and Penicillium.

I claim:

1. Process for producing citric acid b fermentation, which process consists in cu fermentation whic tivating citric acid producers ion molasses at a tenperature between the limits of'15 and 30 selecting cultures adapted for conducting the citric acid fermentation without production of oxalic acid and growin the selected cultures-which cannot be distinguished on morphological grounds from other strains of the same speciesupon a culture medium'made-up from molasses.

2. Process for producing citric acid b fermentation, which process consists in cu1t1-. vating citric acid producers on molasses at a tem erature between the limits of 15 and 30 selecting cultures adapted for conducting the citrlc acid fermentation without production of oxalic acid and growing the selected cultures-which cannot be distinguished on morphological grounds from other strains of the same species-upon a culture medium made up from molasses guished on morphological grounds from other strains of the same species-upon a culture medium made up from molasses with an addition of nutrient salts and recovering the produced citric acid from the fermente liquor by interaction of compounds forming insoluble citric acid salts.

4. Process for roducing citric acid b process consists in cu tivating citric acid producers on molasses at a temperature between the limits of 15 [and 30 (3., selecting cultures adapted for conducting the citric acid fermentation without production of oxalic acid and growing the selected cultureswhich cannot be distinguished on morphological grounds from other strains of the same species--upon a culture medium made up from molasses with an addition ofnutrient salts, and recovering the produced citric acid from the fermented liquor by neutralisation with compounds of barium.

5. Process for producing citric acid b fermentation,,which process consists in on tivating citric acid producers on molasses at a temperature between the limits of 15 and 30 (3., selecting cultures adapted for con ducting the-citric acid fermentation without production of oxalic'acid and growing the selected cultures-which cannot be distinguished on morphologicalgrounds from other strains of the same species-upon a culture medium made up from molasses with an addition of nutrient salts, and recovering the produced citric acid from the fermented liquor at the rate of its formation III during fermentation by neutralization with l at a temperature between the limits of compounds of barium. 15 and 30 C.. and recovering the citric acid 6. The process for producing citric acid produced from the fermented liquor. 10 by fermentation, which consists in employ- In testimony whereof I have afiixed my 8 ing molasses as culture medium, conducting aignltufl- 4 the fermentation with strains from citric producers by cultivation on mo- JOSEF SZUCS. 1 e 

